The Electoral Commission has concluded that there was no widespread evidence of voting fraud at last year's local and general elections, despite allegations at the time that the postal ballot system was being exploited.

More than 200 cases of alleged electoral fraud were reported to the police ahead of elections in May, prompting the Electoral Commission to investigate whether the suspected practice was more widespread.

But in a report published today the commission says that only one of the 232 cases resulted in a conviction and concludes that there is "no evidence to date of any widespread, systematic attempts to undermine or interfere with the 2010 elections through malpractice".

Critics have attacked the report as a whitewash, stating that the lack of successful prosecutions simply highlights how difficult it can be to investigate voting irregularities.

Rob Hoveman, an election agent for the Respect Party, which claimed postal-ballot rigging was commonplace in East London, said: "The fact is that it remains very easy for votes to be cast through personation, for false voters to be registered and, above all, for undue, inappropriate and illegal pressure to be applied in the casting of postal votes through the postal vote on demand system."

He added: "Just because a crime hasn't been prosecuted doesn't mean a crime didn't take place."

Peter Golds, Conservative councillor for Blackwall and Cubitt Town, added: "I can't quite believe the Electoral Commission is being so dismissive of the problems with the voting system. It required more security for me to attend the counting of the vote than it did to cast my vote."

Numerous allegations of electoral fraud were made in the run-up to the general election by all political parties. There was particular concern over postal ballots which voters are still able to apply for without providing any identification. In some constituencies, concerns were raised over properties with surprisingly high numbers of people registered to vote, often in houses with just one or two bedrooms.

On 4 May a reporter from The Independent was assaulted by a gang of youths while investigating allegations of electoral fraud in East London. Jerome Taylor knocked on the door of Khales Uddin Ahmed, a prospective Labour councillor in the Bromley-by-Bow ward who had 12 people registered at his address, seven of whom had been added to the electoral roll in the eight weeks prior to the election.

Two of the people who assaulted Mr Taylor ran into Mr Ahmed's house afterward. Nobody has been charged over the incident. There is no mention of this in the report into electoral fraud. Instead, the report blames the media for "creating a climate where people think malpractice is more prevalent than it is". Of the 232 cases referenced in the report, 68 remain under investigation while 23 resulted in the police offering informal advice to the alleged culprits. Two cautions were issued, while one case is making its way through the courts. The other 137 complaints were dropped.

The only conviction was for Terry Daley, of Coningsbury Drive, Manchester, who was fined £200 for handing out leaflets which claimed that Labour candidate John Flanagan was "corrupt". Mr Daley said he was paid to hand out the leaflets by a man and a women he did not know.